SATELLITE NETWORKS by wulinqing

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									   SATELLITE NETWORKS


             Ian F. Akyildiz

   Broadband & Wireless Networking Laboratory
   School of Electrical and Computer Engineering
           Georgia Institute of Technology
       Tel: 404-894-5141; Fax: 404-894-7883
              Email: ian@ece.gatech.edu
Web: http://www.ece.gatech.edu/research/labs/bwn
        Why Satellite Networks ?
   Wide geographical area coverage
   From kbps to Gbps communication everywhere
   Faster deployment than terrestrial infrastructures
   Bypass clogged terrestrial networks and are oblivious to
    terrestrial disasters
 Supporting both symmetrical and asymmetrical
    architectures
 Seamless integration capability with terrestrial networks
 Very flexible bandwidth-on-demand capabilities
 Flexible in terms of network configuration and capacity
    allocation
 Broadcast, Point-to-Point and Multicast capabilities
 Scalable
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             Orbits
Defining the altitude where the satellite will
 operate.

Determining the right orbit depends on
 proposed service characteristics such as
 coverage, applications, delay.


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                Orbits (cont.)
                                             GEO (33786 km)

GEO: Geosynchronous Earth Orbit
                                       Outer Van Allen Belt (13000-20000 km)
MEO: Medium Earth Orbit
LEO: Low Earth Orbit
                                                     MEO ( < 13K km)




                                  
                                             LEO ( < 2K km)

                                      Inner Van Allen Belt (1500-5000 km)




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                       Types of Satellites
                                         GEO: 33786 km
 Geostationary/Geosynchronous Earth
  Orbit Satellites (GSOs)
  (Propagation Delay: 250-280 ms)

 Medium Earth Orbit Satellites (MEOs)                          LEO: < 2K km
  (Propagation Delay: 110-130 ms)                        (Globalstar, Iridium, Teledesic)


 Highly Elliptical Satellites (HEOs)
  (Propagation Delay: Variable)

 Low Earth Orbit Satellite (LEOs)
                                           
  (Propagation Delay: 20-25 ms)

                                           MEO: < 13K km (Odyssey, Inmarsat-P)




       IFA’2004                                                                         5
      Geostationary/Geosynchronous Earth
      Orbit Satellites (GSOs)

 33786 km equatorial orbit
 Rotation speed equals Earth rotation speed
   (Satellite seems fixed in the horizon)
 Wide coverage area
 Applications (Broadcast/Fixed Satellites,
  Direct Broadcast, Mobile Services)




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           Advantages of GSOs

 Wide coverage
 High quality and Wideband communications
 Economic Efficiency
 Tracking process is easier because of its
  synchronization to Earth




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           Disadvantages of GSOs

 Long propagation delays (250-280 ms).
  (e.g., Typical Intern. Tel. Call  540 ms round-trip delay.
  Echo cancelers needed. Expensive!)
  (e.g., Delay may cause errors in data;
  Error correction /detection techniques are needed.)
 Large propagation loss. Requirement for high
  power level.
  (e.g., Future hand-held mobile terminals have limited power
  supply.)
  Currently: smallest terminal for a GSO is as large as an A4 paper
  and as heavy as 2.5 Kg.


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      Disadvantages of GSOs (cont.)

 Lack of coverage at Northern and Southern
  latitudes.
 High cost of launching a satellite.
 Enough spacing between the satellites to avoid
  collisions.
 Existence of hundreds of GSOs belonging to
  different countries.
 Available frequency spectrum assigned to GSOs
  is limited.

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           Medium Earth Orbit Satellites (MEOs)


Positioned in 10-13K km range.
Delay is 110-130 ms.
Will orbit the Earth at less than 1 km/s.
Applications
    – Mobile Services/Voice (Intermediate Circular
      Orbit (ICO) Project)
    – Fixed Multimedia (Expressway)


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           Highly Elliptical Orbit Satellites (HEOs)


From a few hundreds of km to 10s of
 thousands  allows to maximize the
 coverage of specific Earth regions.
Variable field of view and delay.
Examples: MOLNIYA, ARCHIMEDES
 (Direct Audio Broadcast), ELLIPSO.


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           Low Earth Orbit Satellites (LEOs)

 Usually less than 2000 km (780-1400 km are favored).
 Few ms of delay (20-25 ms).
 They must move quickly to avoid falling into Earth
   LEOs circle Earth in 100 minutes at 24K km/hour.
  (5-10 km per second).
 Examples:
   – Earth resource management (Landsat, Spot, Radarsat)
   – Paging (Orbcomm)
   – Mobile (Iridium)
   – Fixed broadband (Teledesic, Celestri, Skybridge)

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      Low Earth Orbit Satellites (LEOs)
      (cont.)

 Little LEOs: 800 MHz range
 Big LEOs: > 2 GHz
 Mega LEOs: 20-30 GHz




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      Comparison of Different Satellite
      Systems

                            LEO        MEO        GEO


       Satellite Life       3-7        10-15      10-15
       Hand-held Terminal   Possible   Possible   Difficult
       Propagation Delay    Short      Medium     Long
       Propagation Loss     Low        Medium     High
       Network Complexity Complex      Medium     Simple
       Hand-off             Very       Medium     None
       Visibility of a      Short      Medium     Mostly
       Satellite                                  Always



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      Comparison of Satellite Systems
      According to their Altitudes (cont.)




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           Why Hybrids?
 GSO + LEO
   – GSO for broadcast and management
     information
   – LEO for real-time, interactive
 LEO or GSO + Terrestrial Infrastructure
   – Take advantage of the ground
     infrastructure

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           Frequency Bands
NarrowBand Systems
 L-Band  1.535-1.56 GHz DL;
           1.635-1.66 GHz UL
 S-Band  2.5-2.54 GHz DL;
           2.65-2.69 GHz UL
 C-Band  3.7-4.2 GHz DL;
           5.9-6.4 GHz UL
 X-Band  7.25-7.75 GHz DL;
           7.9-8.4 GHz UL

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      Frequency Bands (cont.)
WideBand/Broadband Systems
 Ku-Band  10-13 GHz DL;
             14-17 GHz UL
  (36 MHz of channel bandwidth; enough for
  typical 50-60 Mbps applications)
 Ka-Band  18-20 GHz DL;
             27-31 GHz UL
  (500 MHz of channel bandwidth; enough for
  Gigabit applications)

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             Next Generation Systems:
             Mostly Ka-band

 Ka band usage driven by:
   – Higher bit rates - 2Mbps to 155 Mbps
   – Lack of existing slots in the Ku band
 Features
   – Spot beams and smaller terminals
   – Switching capabilities on certain systems
   – Bandwidth-on-demand
 Drawbacks
   – Higher fading
   – Manufacturing and availability of Ka band devices
   – Little heritage from existing systems (except ACTS and Italsat)


    IFA’2004                                                           19
      Frequency Bands (cont.)
New Open Bands (not licensed yet)
GHz of bandwidth
 Q-Band  in the 40 GHz
 V-Band  60 GHz DL;
         50 GHz UL



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      Space Environment Issues

Harsh  hard on materials and
 electronics (faster aging)
Radiation is high (Solar flares and other
 solar events; Van Allen Belts)
Reduction of lifes of space systems
 (12-15 years maximum).


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           Space Environment Issues (cont.)


 Debris (specially for LEO systems)
  (At 7 Km/s impact damage can be important.
  Debris is going to be regulated).
 Atomic oxygen can be a threat to materials
  and electronics at LEO orbits.
 Gravitation pulls the satellite towards earth.
 Limited propulsion to maintain orbit (Limits
  the life of satellites; Drags an issue for LEOs).
 Thermal Environment again limits material
  and electronics life.
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               Basic Architecture




        LAN                                                  Wireless
                                                            Terrestrial
                                      Ring                   Network
   Mobile
   Network

  Internet       Ring                Internet              Public
                                                           Network
                          MAN
    Ethernet                                    Ethernet

               SIU- Satellite Interworking
               SIU - Satellite Interface Unit Unit
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           Basic Architecture (cont.)




              SIU - Satellite Interworking Unit
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           Satellite Interworking Unit (SIU)




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           Payload Concepts
Bent Pipe Processing
Onboard Processing
Onboard Switching




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        Bent-Pipe Protocol Stack
        (Internet)

                  Satellite   Physical

      Applications                          Applications

           TCP                                  TCP

           IP                                    IP

       Network                               Network
   Medium Access Control                 Medium Access Control
     Data Link Control                     Data Link Control

        Physical                             Physical

  User Terminal                          User Terminal
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           Onboard Processing
           Protocol Stack (Internet)
                              Medium Access Control
                                Data Link Control
                  Satellite
                                  Physical
      Applications                                       Applications

           TCP                                               TCP

           IP                                                 IP

       Network                                            Network
   Medium Access Control                              Medium Access Control
     Data Link Control                                  Data Link Control

        Physical                                          Physical

  User Terminal                                       User Terminal
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             Onboard Switching
             Protocol Stack (Internet)
                               Network
                           Medium Access Control
             Satellite       Data Link Control

      Applications             Physical               Applications

           TCP                                            TCP

           IP                                              IP

       Network                                         Network
   Medium Access Control                           Medium Access Control
     Data Link Control                               Data Link Control

        Physical                                       Physical

  User Terminal                                    User Terminal
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                Routing Algorithms for
                Satellite Networks
                                             Satellites organized in planes
                                             User Data Links (UDL)
                                             Inter-Satellite Links (ISL)
                                             Short roundtrip delays
                                             Very dynamic yet predictable
                                              network topology
                                              – Satellite positions
                                              – Link availability
                                           Changing visibility from the
                                            Earth

http://www.teledesic.com/tech/mGall.htm

   IFA’2004                                                                30
                          LEO’s at Polar Orbits
                                                       Seam
                                                           – Border between
                                                             counter-rotating
                                                             satellite planes
                                                       Polar Regions
                                                           – Regions where the
                                                             inter-plane ISLs are
                                                             turned off
       E. Ekici, I. F. Akyildiz, M. Bender, “The Datagram Routing Algorithm for Satellite IP Networks” ,
                            IEEE/ACM Transactions on Networking, April 2001.

       E. Ekici, I. F. Akyildiz, M. Bender, “A New Multicast Routing Algorithm for Satellite IP Networks”,
                            IEEE/ACM Transactions on Networking, April 2002.
           IFA’2004                                                                                 31
      Routing in Multi-Layered
         Satellite Networks




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           Iridium Network




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           Iridium Network (cont.)




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           Iridium Network (cont.)
   6 orbits
   11 satellites/orbit
   48 spotbeams/satellite
   Spotbeam diameter = 700 km
   Footprint diameter = 4021km
   59 beams to cover United States
   Satellite speed = 26,000 km/h = 7 km/s
   Satellite visibility = 9 - 10 min
   Spotbeam visibility < 1 minute
 System period = 100 minutes

IFA’2004                                     35
           Iridium Network (cont.)
   4.8 kbps voice, 2.4 Kbps data
   TDMA
   80 channels /beam
   3168 beams globally (2150 active beams)
   Dual mode user handset
   User-Satellite Link = L-Band
   Gateway-Satellite Link = Ka-Band
   Inter-Satellite Link = Ka-Band


IFA’2004                                      36
           Operational Systems
       Reference              EUTELSAT     INTELSAT
       Type                   Bent Pipe    Bent Pipe
       Orbit                  GSO          GSO
       Investors              Eutelsat     Intelsat
       Prime                  Various      Various
       Services               Multimedia   Voice, Data, Video Conf.
       Frequencies            Ku           Ku
       Antennas (cm)          120+         120+
       U/L Rates (Mbps)       0.016-2      0.016-2
       Number of Satellites   1            26
       Primary Access         FDMA/TDMA    FDMA/TDMA
       Multibeam              No           No
       ISLs                   No           No
       Transport Protocol     IP/ATM       IP


IFA’2004                                                              37
           Operational Systems (cont.)
           Little LEOs

 Reference         ORBCOMM       VITASAT       STARNET

 Type              Bent Pipe     Bent Pipe     Bent Pipe

 Altitude (km)     775           1000          1000

 Coverage          Below 1 GHz   Below 1 GHz   Below 1 GHz

 Number of         36            24            24
 Satellites
 Mass of           40            150           150
 Satellites (kg)

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                 Proposed and Operational
                 Systems
1.   ICO Global Communications (New ICO)
           Number of Satellites:                           10
           Planes:                                                   2
           Satellites/Plane:                               5
           Altitude:                                       10,350 km
           Orbital Inclination:                            45°
           Remarks:
              Service: Voice @ 4.8 kbps, data @ 2.4 kbps and higher
              Operation anticipated in 2003
              System taken over by private investors due to financial difficulties
              Estimated cost: $4,000,000,000
              163 spot beams/satellite, 950,000 km2 coverage area/beam,
               28 channels/beam
              Service link:   1.98-2.01 GHz (downlink), 2.17-2.2 GHz (uplink); (TDMA)
              Feeder link:    3.6 GHz band (downlink), 6.5 GHz band (uplink)
         IFA’2004                                                                        39
              Proposed and Operational
              Systems (cont.)
2. Globalstar
        Number of Satellites:                          48
        Planes:                                         8
        Satellites/Plane:                               6
        Altitude:                                    1,414 km
        Orbital Inclination:                           52°
        Remarks:
           Service: Voice @ 4.8 kbps, data @ 7.2 kbps
           Operation started in 1999
           Early financial difficulties
           Estimated cost: $2,600,000,000
           16 spot beams/satellite, 2,900,000 km2 coverage area/beam,
            175 channels/beam
           Service link:   1.61-1.63 GHz (downlink), 2.48-2.5 GHz (uplink); (CDMA)
           Feeder link:    6.7-7.08 GHz (downlink), 5.09-5.25 GHz (uplink)
      IFA’2004                                                                        40
           Proposed and Operational
           Systems (cont.)
3. ORBCOM
      Number of Satellites:                         36
      Planes:                                       4                  2
      Satellites/Plane:                             2                  2
      Altitude:                                     775 km             775 km
      Orbital Inclination:                          45°                 70°
      Remarks:
         Near real-time service
         Operation started in 1998 (first in market)
         Cost: $350,000,000
         Service link:  137-138 MHz (downlink), 148-149 MHz (uplink)
         Spacecraft mass: 40 kg



     IFA’2004                                                                    41
           Proposed and Operational
           Systems (cont.)
4. Starsys
     Number of Satellites:                            24
     Planes:                                           6
     Satellites/Plane:                                 4
     Altitude:                                  1,000 km
     Orbital Inclination:                             53°
     Remarks:
         Service: Messaging and positioning
         Global coverage
         Service link: 137-138 MHz (downlink), 148-149 MHz (uplink)
         Spacecraft mass: 150 kg

   IFA’2004                                                            42
            Proposed and Operational
            Systems (cont.)
5. Teledesic (original proposal)
       Number of Satellites:                           840 (original)
       Planes:                                           21
       Satellites/Plane:                                 40
       Altitude:                                        700 km
       Orbital Inclination:                             98.2°
       Remarks:
          Service: FSS, provision for mobile service
                     (16 kbps – 2.048 Mbps, including video) for 2,000,000 users
          Sun-synchronous orbit, earth-fixed cells
          System cost: $9,000,000,000 ($2000 for terminals)
          Service link:    18.8-19.3 GHz (downlink), 28.6-29.1 GHz (uplink) (Ka band)
          ISL: 60 GHz
          Spacecraft mass: 795 kg
      IFA’2004                                                                           43
            Proposed and Operational
            Systems (cont.)
6. Teledesic (final proposal)
       Number of Satellites:                           288 (scaled down)
       Planes:                                          12
       Satellites/Plane:                                24
       Altitude:                                       700 km
       Remarks:
          Service: FSS, provision for mobile service
                     (16 kbps – 2.048 Mbps, including video) for 2,000,000 users
          Sun-synchronous orbit, earth-fixed cells
          System cost: $9,000,000,000 ($2000 for terminals)
          Service link:    18.8-19.3 GHz (downlink), 28.6-29.1 GHz (uplink) (Ka band)
          ISL: 60 GHz
          Spacecraft mass: 795 kg


      IFA’2004                                                                           44
                 References

Survey Paper
  •     Akyildiz, I.F. and Jeong, S., "Satellite ATM Networks: A
        Survey," IEEE Communications Magazine, Vol. 35, No. 7,
        pp.30-44, July 1997.




      IFA’2004                                                45

								
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